94 - FECUNDATION ; HETEROGAMETES. 



VAUCHERIA. 



With the possible exception of Sphceroplea annulina var. braunii, 

 we have dealt thus far with heterogamous fecundation in those algse 

 with uninucleate cells. We shall now examine the sexual process in 

 three notable types, one from among the alga3 and two from the fungi, 

 namely, Vaucheria, Albugo (Cyst opus), and Achlya, in which the 

 cells are multinucleate. 



In the species under consideration, Vaucheria clavata, both anthe- 

 ridia and oogonia may be considered as short side branches cut off 

 from the parent filament by transverse septa. The primordium of the 

 antheridium (Oltmann's, '95) contains numerous small nuclei which 

 probably multiply by division. After the formation of the transverse 

 wall, the nuclei become spindle-shaped, move into the central vacuole, 

 and assume a radial arrangement. Each spindle-shaped body sur- 

 rounded by a court of fine cytoplasm free from chlorophyll represents 

 a spermatozoid. Very fine threads visible in the antheridium were 

 regarded as cilia. 



Concerning the r61e of the nuclei during the development of the 

 oogonium, the several authors differ somewhat. According to Schmitz 

 ('79) the numerous nuclei present in the young oogonium probably 

 fuse later into one. Similar results were obtained by Behrens ('90). 

 Schmitz ('83) claimed that, in the plasmic mass extruded on the 

 opening of the oogonium, small nuclear fragments were present, 

 which had probably become separated from the nuclei of the young 

 oogonium. Klebahn ('92) disputed the above conclusions and asserted 

 that, long after fecundation, he had observed numerous nuclei in each 

 oospore. Oltmanns ('95), using more exact methods, found that a 

 union of the several nuclei in the young oogonium does not take place, 

 but, on the contrary, all save one pass back into the parent filament 

 before the formation of the transverse wall cutting off the oogonium. 

 The development of the oogonium, according to Oltmanns, is as 

 follows : Together with the protoplasmic mass numerous nuclei pass 

 into the primordium of the oogonium (Oogonanlage) (Fig. 34, A). 

 The nuclei, which are in the neighborhood of the future beak, prob- 

 ably undergo division, thereby increasing their number. As soon as 

 the oogonium has reached its definite size, a retreating movement of 

 the plasmic mass sets in, and a portion of the plasma, with numerous 

 chloroplasts and nuclei, re-enters the mother-filament (Fig. 34, B). 

 The single nucleus remaining tarries awhile in the beak at the bound- 

 ary between the colorless and chlorophyll-bearing plasma, but finally 





